Terminal Blocks

On either side of the BFF are 0.1" / 2.54mm pitch terminal blocks. They are broken out for each pin on the plugged in QT Py or Xiao board.

Socket Headers

On either side of the BFF are double-wide socket headers. This lets you plug in a QT Py or Xiao board and then have a socket pin free on every pin for plugging in wires.

STEMMA QT Port

At the bottom edge of the BFF is the STEMMA QT port. These connectors allow you to connect to hundreds of displays, sensors, etc. with STEMMA QT (JST SH) connectors on 3V / GND / SDA / SCL. No pullups are included on the BFF - but most boards have their own.

The SDA and SCL pins are connected to the SDA and SCL pins on a default QT Py pinout. Note that this may differ from the STEMMA QT I2C connection on a QT Py board. For example, the QT Py ESP32-S3 has its STEMMA QT I2C port on pins IO41 (SDA1) and IO40 (SCL1), but its onboard GPIO I2C pins are IO7 (SDA0) and IO6 (SCL0).

Battery Charging

• JST-PH - The battery JST-PH connector, located at the top edge of the BFF, enables you to plug in any 3.7V/4.2V LiPoly battery to the BFF. The BFF will auto-switch to USB power when plugged in via a connected QT Py or Xiao, and charge the battery with extra power.
• +250mA jumper - On the back of the BFF is a jumper labeled +250mA. If you solder this jumper closed, the charge rate will be changed from the default 250mA rate to 500mA (default 250mA + 250mA = 500).
• Disable jumper - On the back of the BFF is a jumper labeled Disable. If you cut this jumper, LiPoly battery charging will be disabled. This will let you use non-rechargeable batteries like AA's in a battery pack with JST PH connector.

LEDs

• DON - On the left side of the board, above the socket headers, is the done charging LED. It is a green LED. It will light up when a connected battery is fully charged.
• CHG - On the right side of the board, above the socket headers, is the charging status LED. It is an orange LED. It will light up when a connected battery is charging via USB.